Added customizable event batch size support to mapparserstream.
Dropped setting id function on selections in renderer since we never go back and update them anyway.
- Updated xhr read stream to use utf8 encoding and to maintain a buffer in order to respect back pressure.
- Updated cellRenderStream to use space() to space out calls to next() so that it provides back pressure and does not overwhelm the browser with continuous DOM element creation.
- Updated parserStream to use a batch size.